The present invention relates to an energy absorber and to an assembly constituted by an energy absorber and a rigid beam.
A bumper comprises an outer decorative covering, referred to as a xe2x80x9cskinxe2x80x9d, and an inner system for absorbing energy which, by deforming, consumes as much as possible of the energy of an impact so as to transmit as little as possible thereof to the vehicle.
In terms of impact, car manufacturers implement a set of specifications that envisage three categories of impact, namely: high speed impacts corresponding to a head-on impact of the vehicle against a rigid or deformable obstacle at a speed of 56 kilometers per hour (km/h) to 64 km/h, xe2x80x9cinsurancexe2x80x9d impacts such as those known as xe2x80x9cDannerxe2x80x9d impacts, at 15 km/h against a fixed wall, and small impacts or xe2x80x9cparking bumpsxe2x80x9d at a speed lying in the range 4 km/h to 8 km/h, such as defined in the standard ECE R42.
High speed impacts are taken into consideration for the purpose of protecting the occupants of the vehicle, whereas xe2x80x9cinsurancexe2x80x9d and xe2x80x9cparkingxe2x80x9d impacts, i.e. xe2x80x9csmallxe2x80x9d impacts correspond rather to the purpose of reducing repair costs.
High speed impacts are managed by associating the structure of the vehicle with safety systems that are included in the vehicle cabin.
xe2x80x9cInsurancexe2x80x9d impacts are managed by combining siderail extenders with the impact beam of the vehicle;
xe2x80x9cParkingxe2x80x9d bumps are sometimes managed by absorber systems placed between the skin and the beam of the vehicle, in the form of injected honeycomb structures.
The above types of impact are now associated with new requirements relating to impacts against pedestrians. Managing a pedestrian impact requires systems to be made more flexible and for them to behave in uniform manner over the entire width of the vehicle since such an impact must protect the pedestrian""s legs so as to limit severe and handicapping injuries. For this purpose, it is general practice to use a foam obtained by expanding a thermoplastic (polyphenylene ether (PPE) foam).
To reconcile the requirements relating to the above-mentioned impacts with those relating to pedestrian impacts, it is common practice to make a stack of a traditional system with a layer of foam. The foam absorbs the energy of pedestrian impacts, while the traditional system operates in the event of a higher energy impact, after the foam has been pressed in.
One of the problems with such a stack is its cost, which is very high, particularly because of the cost of the foam and of the handling that is needed for putting it into place on the system.
Another problem results from the depth which is needed to make the layer of foam effective. This dimension is directly related to the intrinsic characteristics of the material which define its ability to absorb energy and its maximum compression ratio. This leads to the front of the vehicle being made relatively large.
The present invention seeks to propose a novel configuration for absorbers that comply with requirements concerning impacts in all of the above-mentioned categories of impact, but which is particularly simple and much less expensive to implement.
The present invention provides an energy absorber for interposing between a bumper skin and a rigid beam, the beam having a bearing surface and at least one corner that presents an escape surface, the function of the energy absorber being to absorb by compression the energy of impacts directed along a crumpling direction and the absorber comprising a set of ribs, each of which extends parallel to the crumpling direction and presents a free edge for bearing against the beam.
In this energy absorber, said set of ribs comprises at least one rib arranged, in the event of an impact, so that its free edge remains pressed against the beam while said rib buckles, and at least one rib arranged in such a manner that in the event of an impact its free end begins by escaping from the beam by sliding over the escape surface, after which said rib slides over the corner of the beam and bends, moving further and further away from the crumpling direction.
The energy absorber of the invention does not require the presence of any foam and it can be obtained directly by molding plastics material under the same conditions as apply to molding the prior art honeycomb structure.
That is why the energy absorber of the invention is very inexpensive to provide.
The originality of the energy absorber of the invention lies in the fact that it has two types of rib, namely: one or more buckling ribs which, as in a honeycomb, absorb impact energy by compressing axially, and bending ribs which, unlike honeycomb ribs, slide over the corner of the beam with a friction force that increases as the beam gets closer to the base of the rib in question, since said rib forms an increasing angle relative to the direction of impact.
The advantage of these bending ribs is that they provide resistance to deformation that increases with increasing deformation of the energy absorber, which behavior is the converse of that of a buckling rib.
This makes it possible to reproduce the behavior of a foam without needing to use such a material.
In a particular embodiment of the invention, at least one of the ribs has a base portion, remote from its free edge, and provided with transverse stiffener means.
These transverse stiffening means reconstitute a honeycomb structure in the base portion of the rib.
In the invention, it is important for this base portion to extend over part of the rib only, since the rib must also have an end portion suitable for buckling or for bending in the vertical direction.
The invention also provides an assembly constituted by an energy absorber and a rigid beam having a bearing surface and at least one corner presenting an escape surface, for placing behind a bumper skin to absorb impact energy directed in a crumpling direction, the energy absorber comprising a set of ribs each of which extends parallel to the crumpling direction and possesses a free edge bearing against the beam, wherein the bearing surface of the beam is shaped in such a manner that the free edge of one rib cannot slide laterally over the beam in the event of crumpling in the crumpling direction, such that said rib buckles, wherein the corner of the beam is shaped in such a manner that in the event of crumpling in the crumpling direction, the free edge of a rib of the energy absorber escapes laterally from the beam by sliding over the escape surface, said rib then sliding over the corner and bending while moving further and further away from the crumpling direction, and wherein said set of ribs includes at least one rib arranged so that its edge bears against said corner surface of the beam, and at least one rib arranged so that its free edge bears against said bearing surface of the beam.
Advantageously, the bearing surface of the beam is constituted by a concave shape which holds the free ends of the ribs that are designed to buckle in order to prevent them from escaping from the beam, and thus prevent them from behaving like bending ribs.